This invention relates to a process for the recovery of hydrogen iodide and more particularly to a process for the recovery of relatively anhydrous hydrogen iodide from a mixture containing hydrogen iodide, water and iodine.
U.S. Pat. No. 4,089,940, issued May 16, 1978 to Norman et al., discloses a process for the thermochemical production of hydrogen which is based upon the employment of the Bunsen reaction: 2H.sub.2 O+SO.sub.2 +I.sub.2 .fwdarw.H.sub.2 SO.sub.4 +2HI. In this process, the Bunsen reaction is carried out using an excess of iodine in order to create a twophase reaction mixture. The lower phase of this mixture, which is then physically separated from the upper phase, contains the major portion of the hydrogen iodide that is produced together with water and iodine. In order to efficiently recover elemental hydrogen from the hydrogen iodide component of this mixture, using a catalytic decomposition reaction or the like, it is felt necessary to first isolate relatively anhydrous hydrogen iodide.
U.S. Pat. No. 4,127,644, which issued on Nov. 28, 1978 to Norman et al., discloses an extractive distillation process for recovering hydrogen iodide from a liquid mixture of H.sub.2 O, I.sub.2 and HI which utilizes phosphoric acid to generate a vapor stream of relatively anhydrous HI. Extractive distillation is an energy-intensive processing step and the subsequent reconcentration of the phosphoric acid is also a fairly energy-intensive step. Less energy-intensive steps or minimization of the use of such energy-intensive steps are desired.
U.S. patent application Ser. No. 921,435, filed July 3, 1978 in the name of Karol J. Mysels, now U.S. Pat. No. 4,176,169, teaches a process for the countercurrent extraction of iodine from a liquid solution containing iodine, hydrogen iodide and water by employing concentrated phosphoric acid. The percentage of iodine in such a liquid solution can be substantially reduced; of course H.sub.3 PO.sub.4 is added to the solution as a result. This countercurrent extraction process can be employed preliminary to an extractive distillation process wherein a relatively anhydrous hydrogen iodide overhead stream is produced. Although such a combination of processes is less energy-intensive than effecting the entire separation through extractive distillation, work has continued in a search for further improvements.